The underlying epigenetic mechanisms that govern cell-fate determination and pluripotency during early embryonic development are poorly understood. The long-term goal is to better understand the chromatin-based mechanisms that regulate gene expression changes between days 2.5 (8-cell) to 6.5 (pre-gastrulation) of mouse embryonic development. These stages of development in a mouse model correspond to the stages of development in humans when a large percentage of embryos are lost to either failed implantation or early miscarriage. The overall objective of this application is to investigate the specific role of the Brg1 chromatin-remodeling protein in trophectoderm development and pluripotency. Brg1 is a critical chromatin-remodeling enzyme that is implicated in human cancer and mammalian development. Brg1-deficient embryos arrest around the blastocyst stage, undergo perturbations in gene expression, and exhibit defects in the ICM and trophectoderm. Moreover, disruption of Brg1 function in embryonic stem (ES) cells results in phenotypic changes indicative of differentiation, downregulation of self-renewal and pluripotency genes, and upregulation of differentiation genes. The specific aims of this application are to test the hypotheses that: 1) Brg1 is required for epigenetic silencing of Oct4 and Nanog expression in the trophectoderm. 2) Brg1 and Nanog promote embryonic pluripotency through epigenetic regulation of Oct4 and Klf5. To address these questions a battery of molecular, cellular, and biochemical assays will be performed in vitro and in vivo. These will include microinjection of siRNAs and mRNAs, immunocytochemistry, chromatin immunoprecipitation (ChIP) assays, chromatin- remodeling assays, and real-time qPCR analysis. The proposed studies will enhance our basic knowledge of early mammalian development. Moreover, these studies are relevant to clinical infertility, human oncology, and stem cell differentiation for cell replacement therapies.